Chloride-hydride Vapor-phase Epitaxy Research Articles

The Electrical Properties of Schottky Barrier Diode Structures Based on HVPE Grown Sn Dopped Ga2O3 Layers

We report on the analysis of the electrical properties of Schottky barrier diode structures based on gallium oxide (Ga2O3). Ga2O3 has been grown by chloride-hydride vapor phase epitaxy on Al2O3 substrate. Samples with different amounts of Sn impurity are experimentally characterized. Surface and cross-sectional scanning electron microscopy images, X-ray diffraction patterns and current-voltage characteristics of Ga2O3 layers both with and without contact pads are presented. The value of the Ga2O3 optimal doping is determined and the parameters of the surface treatment that is performed before the contact pads deposition are established.

Effect of Pretreatment of the Silicon Substrate on the Properties of GaN Films Grown by Chloride–Hydride Vapor-Phase Epitaxy

Effect of Pretreatment of the Silicon Substrate on the Properties of GaN Films Grown by Chloride–Hydride Vapor-Phase Epitaxy

Особенности пироэффекта в эпитаксиальных слоях нитрида алюминия, полученных на Si-подложках

The pyroeffect was studied in quasi-bulk AlN layers with a thickness of 10-170 μm obtained by the technology of chloride-hydride vapor phase epitaxy on standard Si sub-strates. The pyroelectric current was measured by the method of thermal exposure to non-stationary (me-ander type) laser radiation, that together with the data of independent non-contact measure-ment of the active layer surface temperature dynamics made it possible to determine the value of the pyroelectric coefficient AlN in the composition of the bimorph AlN / Si structure for different thicknesses of AlN layers. It was found that the mean values are less than those that correspond to the material obtained by the same technology, but on SiC substrates; so, in or-der to achieve the pyrocoefficients of comparable magnitude with those in the case of “AlN on Si”, an increase in the thickness of AlN layers by 60 -70% is re-quired. At the same time, when the thickness of the AlN layer is large (110 μm, 170 μm) after the removal of the silicon substrate, the pyroelectric coefficient increased and reached ~8.6-9.0μC/(m2·K).

Method for Controlling the Polarity of Gallium Nitride Layers in Epitaxial Synthesis of GaN/AlN Heterostructures on Hybrid SiC/Si Substrates

The effect of the inversion of polarity in gallium nitride layers from the N-polar GaN layer to the Ga-polar GaN layer was discovered during the sequential growth of GaN films on hybrid SiC/Si(111) substrates by nitrogen plasma-assisted molecular beam epitaxy and chloride–hydride vapor phase epitaxy. A new method has been developed for the formation of crack-free Ga-polar GaN/AlN heterostructures on hybrid SiC/Si(111) substrates. The method includes two stages of growing gallium nitride layers. At the first stage, the transient N-polar GaN layer is grown on the SiC/Si(111) surface by nitrogen plasma-assisted molecular beam epitaxy. At the second stage, two layers are grown on the obtained N-polar GaN layer by chloride–hydride vapor phase epitaxy, namely, the AlN layer and then the GaN layer, which at this stage grows in the Ga-polar orientation. Etching in a KOH solution affects only the N-polar GaN transition layer and leads to its complete removal. This procedure separates the main Ga-polar GaN layer from the SiC/Si(111) substrate completely. The method enables one to grow crack-free and elastically unstressed thick GaN layers and transfer them to substrates of other materials.

Growing III–V Semiconductor Heterostructures on SiC/Si Substrates

A three-layer heterostructure consisting of AlN (∼0.72 μm thick), AlGaN (∼ 1.82 μm thick), and GaN (∼2.2 μm thick) layers has been grown by hydride–chloride vapor phase epitaxy (HVPE) method on a Si substrate with a SiC buffer nanolayer. The heterostructure was studied using scanning electron microscopy, energy-dispersive X-ray spectroscopy, and other techniques. The results showed that SiC/Si substrates can be used for growing films of III–V semiconductor compounds by HVPE at a high rate (~66 μm/h) free of cracks and with small residual elastic stresses (~160 MPa).

New Semipolar Aluminum Nitride Thin Films: Growth Mechanisms, Structure, Dielectric and Pyroelectric Properties

Surface topography, dielectric and pyroelectric properties of semipolar AlN thin films are studied. The growth of AlN was carried out by hydride-chloride vapor phase epitaxy on hybrid SiC layers specially prepared for the growth of semipolar AlN layers. SiC layers were grown on Si substrates of p-type (KDB) with (100)-orientation. The dynamic pyroelectric response of the AlN layer was observed. The pyroelectric current kinetics was analyzed in the frequency range of 10–1000 Hz, and the calculated pyroelectric coefficient was nearly equal to 9·10−10 C/(cm2K).

Asymmetry of the Defect Structure of Semipolar GaN Grown on Si(001)

The defect structure of a thick (~15 μm) semipolar gallium nitride (GaN) layer grown by hydride–chloride vapor phase epitaxy on a Si(001) substrate with buffer layers has been studied by transmission electron microscopy. The asymmetry of the defect structure of GaN epilayer has been revealed and analyzed. The influence of this asymmetry on the rate of decrease in the density of threading dislocations in the growing epitaxial layer is discussed.

Raman Spectra of Thick Epitaxial GaN Layers Formed on SiC by the Sublimation Sandwich Method

The Raman spectra of thick (~100 μm and more) GaN layers grown on crystalline SiC substrates by the sublimation sandwich method are studied. Good agreement between the spectra of the SiC substrates used in the study and published data indicates that the measurements made in the study are reliable. The minimum difference between the results of the measurements and published evidence for GaN layers means that the layers grown by the sublimation sandwich method in the study compare well with those fabricated by the metalorganic vapor phase epitaxy (MOVPE) or chloride-hydride vapor phase epitaxy (CHVPE) techniques.

Studying the Pyroelectric Effect in AlN Epilayers

We have studied the pyroelectric effect in 6- to 12-μm-thick AlN epilayers grown by hydride–chloride vapor phase epitaxy (HVPE) on 4H-SiC substrates. The pyroelectric current was generated by means of dynamic laser action. Evolution of the temperature fields was monitored by direct measurements of the surface temperature with allowance for the specific thermal heterogeneity of the AlN/SiC system. In combination with the results of pyroelectric current measurements, these data allowed the pyrocoefficient of the AlN/SiC structure to be estimated at p ≈ 3.0 μC/(m2 K). Pyroelectric figures of merit of the given structure are calculated that can be used for the comparison of pyroelectric materials intended for the creation of IR radiation detectors.

Исследование пироэффекта в AlN-эпитаксиальных слоях

AbstractWe have studied the pyroelectric effect in 6- to 12-μm-thick AlN epilayers grown by hydride–chloride vapor phase epitaxy (HVPE) on 4H-SiC substrates. The pyroelectric current was generated by means of dynamic laser action. Evolution of the temperature fields was monitored by direct measurements of the surface temperature with allowance for the specific thermal heterogeneity of the AlN/SiC system. In combination with the results of pyroelectric current measurements, these data allowed the pyrocoefficient of the AlN/SiC structure to be estimated at p ≈ 3.0 μC/(m^2 K). Pyroelectric figures of merit of the given structure are calculated that can be used for the comparison of pyroelectric materials intended for the creation of IR radiation detectors.

Асимметрия дефектной структуры полуполярного GaN, выращенного на Si(001)

AbstractThe defect structure of a thick (~15 μm) semipolar gallium nitride (GaN) layer grown by hydride–chloride vapor phase epitaxy on a Si(001) substrate with buffer layers has been studied by transmission electron microscopy. The asymmetry of the defect structure of GaN epilayer has been revealed and analyzed. The influence of this asymmetry on the rate of decrease in the density of threading dislocations in the growing epitaxial layer is discussed.

Спектры рамановского рассеяния толстых эпитаксиальных слоев GaN на SiC, полученных сублимационным сандвич-методом

AbstractThe Raman spectra of thick (~100 μm and more) GaN layers grown on crystalline SiC substrates by the sublimation sandwich method are studied. Good agreement between the spectra of the SiC substrates used in the study and published data indicates that the measurements made in the study are reliable. The minimum difference between the results of the measurements and published evidence for GaN layers means that the layers grown by the sublimation sandwich method in the study compare well with those fabricated by the metalorganic vapor phase epitaxy (MOVPE) or chloride-hydride vapor phase epitaxy (CHVPE) techniques.

Optical properties of bulk gallium nitride single crystals grown by chloride–hydride vapor-phase epitaxy

A gallium nitride crystal 5 mm in thickness was grown by chloride–hydride vapor-phase epitaxy on a sapphire substrate, from which the crystal separated during cooling. At an early stage, a three-dimensional growth mode was implemented, followed by a switch to a two-dimensional mode. Spectra of exciton reflection, exciton luminescence, and Raman scattering are studied in several regions characteristic of the sample. Analysis of these spectra and comparison with previously obtained data for thin epitaxial GaN layers with a wide range of silicon doping enabled conclusions about the quality of the crystal lattice in these characteristic regions.

Semipolar AlN on Si(100): Technology and properties

Initial stages of the semipolar AlN layer formation by chloride-hydride vapor phase epitaxy on a misoriented Si(100) substrate with a thin intermediate nano-SiC layer grown by atomic substitution method are investigated. It is found that once the growth rate of AlN layer on a nano-SiC/Si(100) substrate is about 0.02μm/h, the layer is formed in a polar direction. On the other hand, at the growth rate of 1μm/h the layer is formed in a semipolar direction. We propose the model of the semipolar AlN layer growth based on the formation of the special structure on the SiC layer synthesized by atomic substitution and on the possibility of the matching of the quasi-lattices of Al(20−23) and 3CSiC(100) planes assuming bonding of four atoms from the layer to four atoms of the 3CSiC quasi-lattice consisting of three lattice unit cells in one of the directions.

Photoelectrochemical Corrosion of GaN/AlGaN-Based p-n Structures

Direct water photoelectrolysis using III-N materials is a promising way for hydrogen production. GaN/AlGaN based p-n structures were used as working electrodes in a photoelectrochemical process to investigate the material etching (corrosion). The structures were grown on sapphire substrates by chloride Hydride Vapor Phase Epitaxy (HVPE). First, the etching process occurs near vertically via channels associated with defects in the structure and penetrates deep into the structure. Then, the process involves etching of the n-type AlGaN barrier and n-GaN active layer in lateral direction resulting in formation of voids and cavities. The lateral etching is due to net positive charges at the AlGaN/GaN interfaces arising because of spontaneous and piezoelectric polarization in the structure and positively charged ionized donors in the space charge region of the p-n junction.

Pendeo-epitaxy of stress-free AlN layer on a profiled SiC/Si substrate

A new approach to the pendeo-epitaxy of elastically-unstrained AlN films is developed. The AlN films are grown using chloride-hydride vapor phase epitaxy (HVPE) on a silicon substrate with specially synthesized and shaped buffer layer of nano-SiC (NSiC). This NSiC epitaxial layer is grown using a new technique based on the substitution of a part of silicon atoms by carbon ones in a 100–110nm thick subsurface layer of the silicon substrate. The 2D array of ~200nm in diameter wells with the depth of ~70nm that is less than the NSiC layer thickness is formed on the NSiC surface using electron beam lithography followed by reactive ion etching, the period of the array is of 400nm. In a single HVPE process we grew ~20μm thick AlN film both on the shaped and smooth regions of the prepared substrate. The AlN films are examined with reflection high energy electron diffraction, X-ray diffractometry, Raman spectroscopy and scanning electron microscopy. We use the results of these measurements to compare residual elastic stresses in the AlN film grown on the shaped and smooth regions of the substrate. The film on the shaped part of the substrate is elastically-unstrained contrary to the smooth part where elastic stresses result in the formation of a textured AlN layer. The model of the AlN growth on shaped SiC/Si substrates prepared using the atomic substitution technique is proposed.

Photo-Electrochemical Etching in the Process of Direct H2 Generation by Illumination of GaN-Based Material Structures Immersed in Water

Hydrogen is considered a promising candidate for energy storage. We investigated the cleanest way for hydrogen production by direct photo electrolysis of water with GaN/AlGaN based p-n structures used as working electrodes. Besides the H2 production rate, an important consideration is the material etching (corrosion) that accompanies the photo-electrochemical process. The GaN-based structures were grown on sapphire substrates by the chloride hydride vapor phase epitaxy and used as a photo anode immersed into an aqueous electrolyte. For a p-n GaN/AlGaN structure we observed a H2 production rate of 0.6 mL/cm2×h. Corrosion of the electrode proceeds in two steps. First, there is a near vertical etching process, which is associated with defects in the material and penetrates deep into the structure. Subsequently, the process involves etching of n-type layers in lateral direction resulting in the formation of voids and cavities. The lateral etching is due to net positive charges arising from the spontaneous and piezoelectric polarization in the structure and positively charged ionized donors in the space charge region of the p-n junction.

The effect of surfactants on epitaxial growth of gallium nitride from gas phase in the Ga-HCl-NH3-H2-Ar system

We have studied epitaxial layers of gallium nitride (GaN) in a template composition grown by surfactant-mediated hydride-chloride vapor phase epitaxy. The surfactant component was provided by 5 mass % additives of antimony and indium to the source of gallium. Comparative analysis of the obtained results shows evidence of the positive influence of surfactants on the morphology of epitaxial GaN layers.

Study of the degradation of the external quantum efficiency of UV LEDs based on AlGaN/GaN heterostructures grown by chloride-hydride vapor-phase epitaxy

Final stage of the degradation of the external quantum efficiency of AlGaN/GaN UV light-emitting diodes (LEDs), grown by chloride-hydride vapor-phase epitaxy, and high-power InGaN/GaN blue LEDs, produced by metal-organic vapor-phase epitaxy, has been comparatively studied. It is shown that one of these processes leading to a decrease in the quantum efficiency for both types of LEDs is the local defect formation involving the Gold-Weisberg mechanism in a system of extended defects. To prolong the service life of AlGaN/GaN UV LEDs to more than 2000 h, it is necessary to improve the nanostructural arrangement of the material of light-emitting structures and determine the contribution from the AlGaN composition disorder to the degradation of the external quantum efficiency.

Study of the characteristics of ultraviolet light-emitting diodes based on GaN/AlGaN heterostructures grown by chloride-hydride vapor-phase epitaxy

The results of work on developing and studying ultraviolet (UV) light-emitting diodes (LEDs) based on GaN/AlGaN heterostructures fabricated on Al2O3(0001) substrates by the chloride-hydride vaporphase epitaxy are presented. The maximum in the electroluminescence spectrum is located in the wavelength range of 360–365 nm, and its full width at half maximum is 10–13 nm. At a working current of 20 mA, the optical density and efficiency of the UV LED are 1.14 mW and 1.46%, respectively.